Inhibition of dark spots on freshly spun



United States Patent Ofiice INHIBITION OF DARK SPOTS N FRESHLY SPUN VISCOSE BY WASHING WITH A SPECIFIC SE- QUESTERING AGENT Donald J. Godehn, Hendersonville, N. C., assignor to American Enka Corporation, Enka, N. C., a corporation of Delaware No Drawing. Application November 2, 1955, Serial No. 544,610

8 Claims. (Cl. 8137.5)

This application is a continuation-in-part of application Serial No. 236,459, filed July 12, 1951, now abandoned, which in turn is a continuation-in-part of application Serial No. 134,143, filed December 20, 1949, now abandoned.

The present invention relates to the aftertreatment of viscoserayon packages and more particularly to a method of preventing or inhibiting the formation of dark spots throughout the body of the packages and especially those normally occurring in the areas defined by the surfaces of the rayon packages during the aftertreating thereof.

Broadly, the invention is concerned with the treatment of any type of package formed from freshly spun viscose rayon although it is concerned primarily with those types of packages that are wound on rigid perforated bobbins and thereby acquires a low degree of permeability.

It is the usual practice to wash and desulphur such acid containing spools or packages by forcing suitable treating liquids through the body thereof by the application of a pressure differential to the liquids. The procedure generally adopted is to vacuum and/or pressure wash the acid spools with water at room temperature to remove all of the acid and spinbath salts retained as a result of passing the thread through an acid coagulating bath during the thread forming stage. This washing step is followed by a short hot water wash to remove the carbon bisulphide and is known as the degassing operation. The spools are next treated with a dilute solution of ammonium sulphide or sodium sulphide in order to remove the sulphur content and are finally washed with water to remove the desulphuring liquid;

One of the major difiiculties encountered in washing and desulphuring viscose rayon in package form is due to the presence of certain impurities within the acid thread, some of which are the salts of heavy metals. These salts being only slightly soluble remain in the thread during the usual liquid treatments and are precipitated throughout the packages during the desulphuring operation, causing the finished product to assume a dingy or grey color. Moreover, a small quantity of the impurities follow the direction of flow of the treating liquids and react with the sulphides employed during desulphuring to form dark spots near the surfaces of the packages. If the flow of liquid is from the outside to the inside of the package the dark spots will be near the inside surface, whereas if the fiow is from the inside to the outside, in some cases dark spots may occur near the outside surface of the package.

Prior to the present invention, to preclean a substantial amount of the thread, i. e., several hundred yards of thread containing these dark spots have been removed and couldbe sold only as inferior quality. It is obvious that this precleaning step is time and labor consuming to carry out and is therefore doubly expensive in the process because the inferior thread must be sold ata considerably lower price than it would otherwise demand. Furthermore, even when the inner or outer convolutions were removed, the yarn in the body of the package proper it has been necessary 2,735,742 Patented Feb. 21, 1956 was slightly off-color, i. e., it was not as bright as is desirable.

It is therefore an object of the present invention to prevent or inhibit the formation of dark spots and dinginess in freshly spun packages of viscose rayon during aftertreatments.

A further object of this invention is to provide a process of liquid treating bobbin or cake spun rayon packages by means of applying a pressure differential to the liquids to force the same through the packages and during the liquid treatments, subjecting the packages to the action of an agent that will render the troublesome impurities soluble and inactive whereby they are removed either prior to, during, or after desulphuration.

An additional object of this invention is to wash or desulphur rayon packages with solutions containing an alkali salt of 'alkylene diamine aliphatic, saturated mono basic carboxylic acids to prevent the formation of insoluble heavy metal sulphides.

Other objects and advantages of the present invention will become apparent upon consideration "of the following detailed description.

It has been determined that if during the aftertreatments of the rayon packages certain sequestering or chelating agents are used in one of the treating solutions, the formation of dark spots throughout the packages is prevented and the overall grey color in the yarn is reduced. These agents are alkali salts of alkylene diamine poly aliphatic saturated mono basic carboxylic acids and more particularly the alkali salts of alkylene diamine tetra aliphatic saturated mono basic carboxylic acids having the following structural formula:

wherein M represents an alkali metal or NH4 which resembles an alkali metal, n is zero or a small whole numher not greater than 2, a is a small whole number at least 2 and b is a small whole number at least 1.

As of the present date, the commonest known sequestering agent of this type is the tetra sodium salt of ethylene diamine tetra acetic acid, which is structurally as follows:

NaOOCCHr CHzCOONa N-CH2-CH2- NaOOCC 2 CHZCOONa In applying this specific compound to the above general formula, M is sodium, n is zero, a is 2 and b is 1. This compound is marketed by the Bersworth Chemical Company under the trade name Versene and by the Alrose Chemical Company under the trade name of Sequestrene A. The Alrose Chemical Company also markets a compound known by the trade name Sequestrene Naz diamine tetra acetate dihydrate, or in other words, the hydrogen on two of the carboxyl groups has been replaced by sodium.

These compounds have the ability to molecularly com bine with heavy metals at two or more points by coordinating linkages forming stable and soluble complexes and by so doing effectively remove the heavy metals and their ions from solution. This property of removing heavy metal ions from solutions has caused the compounds to become known as sequestering agents. The heavy metal ion, which is thus bound up is no longer in the ionic state and cannot be precipitated from solution.

It is believed that when a heavy metal such as lead is added to a solution of tetra sodium salt of ethylene diif it In practicing the present process the compound, for example, the tetra sodium salt of ethylene diamine tetra acetic acid, is added in small amounts, i. e., from 0.05% to 0.5%, based on the weight of the solution, to the ammonium sulphide or sodium sulphide solution used in the desulphuring operation. Spools of viscose yarn are then desulphured with this solution in the normal manner, i. e., by vacuum and/or pressure wash, after which the rayon exhibits no spot formation and the yarn as a whole is considerably brighter than the spools that are desulphured without the use of the compound.

Although the compounds can be dissolved and utilized in the water washes preceding the desulphuring operation, it is preferable from a practical standpoint to add the compounds to the desulphuring solution per se because the water washes are normally discarded whereas the desulphuring solution is recirculated and re-used. When these agents are used in an alkaline solution even the acid such as ethylene diamine tetra acetic acid may be employed, which is only slightly soluble in water but forms the salt which is extremely soluble in an alkaline solution.

The slightly soluble heavy metals that are retained in the thread and cause the dark spots and dinginess in the desulphured rayon, are believed to be lead as well as possibly iron. Calcium may also be present. Apparently these metals form stable and soluble complexes with the sequestering agents and are thereby removed either before or during desulphuration because being stable, they cannot be re-precipitated in the presence of the sulphide.

Example 1 Several spools of viscose rayon yarn were removed from the plant vacuum wash two hours prior to the completion of the cold water wash. They were washed in an experimental tank for two hours with an aqueous 0.05% Versene solution at room temperature (23 C.) and then were washed for one and one-half hours with a 0.05% Versene solution maintained at about 65-70 C. The spools were then subjected to the normal desulphuring with ammonium sulphide, re-washed and dried. No spots were observed upon cutting the yarn from the spool and the yarn was noticeably brighter than that of the control sample.

Example 2 Several spools of viscose rayon yarn were removed from the plant vacuum wash prior to desulphuring and washed in a vacuum wash tank for three and one-half hours in the normal ammonium sulphide solution having dissolved therein 0.05% Versene. After the desulphuring operation, the spools were returned to the plant vacuum wash for completion of the normal schedule, dried and twisted. At the same time several control spools from the plant vacuum wash that had been desulphured were washed normally, dried, and twisted for comparison. The control samples were spotted, whereas the spools washed with the sequestering agent exhibited no spots. The control samples were also compared for brightness to those that had been specially treated and there was a distinct improvement in the brightness of the latter which was particularly noticeable on the inside and middle'portions of the packages although there was an improvement in the outside portions.

4 Example 3 Spools of viscose rayon yarn were washed in cold water for 680 minutes. They were then given a minute hot water wash. Next they were desulphured for 240 minutes in an ammonium sulphide solution having dissolved therein 0.2% Versene. The spools were finally re-washed and dried.

Example 4 Spools of viscose rayon yarn were washed in cold water for 680 minutes. They were then washed with hot water for 60 minutes, and next washed for 60 minutes with an aqueous 0.1% Versene solution maintained at a temperature between 60-70 C. The spools were then desulphured in an ammonium sulphide solution for 240 minutes, and finally re-washed and dried.

In each of the above examples, when the spools were unwound, no spots were detected.

Throughout the description, the specific salts have been referred to as sodium salts, because these are the ones most readily available on the market. However, it is within the scope of my invention to use other alkali metal salts such as potassium or an ammonium salt which resembles an alkali metal salt, and any of the alkali metal salts may be di-, tri-, or tetra-substituted. Moreover, the alkylene group may be ethylene, propylene, etc., and the aliphatic, saturated mono basic carboxylic acid may be acetic, propionic, etc.

What is claimed is:

1. In a process in which freshly spun acid viscose rayon packages are washed with water and desulphured with an alkaline sulphide solution whereby dark spots are formed, and dinginess results in the rayon, the step that comprises washing the packages during one of the aftertreating operations with an aqueous solution having dissolved therein a sufficient amount of an alkali metal salt of ethylene diamine poly aliphatic saturated mono basic carboxylic acid selected from the group consisting of acetic and propionic acid and for a period of time and at a temperature sufficient to inhibit the formation of dark spots and dinginess.

2. In a process in which freshly spun acid viscose rayon packages are washed with water and desulphured with an alkaline sulphide solution whereby dark spots are formed, and dinginess results in the rayon, the step that comprises Washing the packages during one of the aftertreating operations with an aqueous solution having dissolved therein a sufiicient amount of an alkali metal salt of ethylene diamine tetra aliphatic saturated mono basic carboxylic acid selected from the group consisting of acetic and propionic acid and for a period of time and at a temperature suflicient to inhibit the formation of dark spots and dinginess.

3. In a process in which freshly spun viscose rayon packages are washed with water and desulphured with an alkaline sulfide solution whereby dark spots are formed, and dinginess results in the rayon, the step that comprises washing the packages before the desulphuring wash is completed with an aqueous solution having dissolved therein at least about 0.05% of a compound consisting essentially of an alkali metal salt of ethylene diamine tetra aliphatic saturated mono basic lower carboxylic acid selected from the group consisting of acetic and propionic acid for a period of time and at a temperature sufficient to inhibit the formation of dark spots and dinginess.

4. The process of claim 3 in which the amount of alkali metal salt of ethylene diamine tetra aliphatic saturated mono basic carboxylic acid added is in a range of 0.05% to 0.5 based on the total weight of the solution.

5. The process of claim 3 in which the alkali metal salt of ethylene diamine tetra aliphatic saturated mono basic carboxylic acid is disodium ethylene diamine tetra acetate dihydrate.

6. The process of claim 3 in which the alkali metal salt of ethylene diamine tetra aliphatic saturated mono basic carboxylic acid is added to the desulphuring solution.

7. A process for inhibiting dinginess and dark spots in freshly spun viscose rayon packages which comprises washing the packages before the desulphuring wash is completed with an aqueous solution having dissolved therein 0.05% to 0.5% based on the total weight of the solution of an organic salt having the following structural formula:

8. The process of claim 7 in which the organic salt is tetra sodium ethylene diamine tetra acetic acid.

References Cited in the file of this patent UNITED STATES PATENTS James May 12, 1953 Fleysher Apr. 5, 1955 OTHER REFERENCES Gard: American Dyestuflf Reporter, December 21, 1953, pages P867-P870. (Copy in Patent Oince Library.) 

1. IN A PROCESS IN WHICH FRESHLY SPUN ACID VISCOSE RAYON PACKAGES ARE WASHED WITH WATER AND DESULPHURED WITH AN ALKALINE SULPHIDE SOLUTION WHEREBY DARK SPOTS ARE FORMED, AND DINGINESS RESULTS IN THE RAYON, THE STEP THAT COMPRISES WASHING THE PACKAGES DURING ONE OF THE AFTERTREATING OPERATIONS WITH AN AQUEOUS SOLUTION HAVING DISSOLVED THEREIN A SUFFICIENT AMOUNT OF AN ALKALI METAL SALT OF ETHYLENE DIAMINE POLY ALIPHATIC SATURATED MONO BASIC CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF ACETIC AND PROPIONIC ACID AND FOR A PERIOD OF TIME AND AT A TEMPERATURE SUFFICIENT TO INHIBIT THE FORMATION OF DARK SPOTS AND DINGINESS. 